Mono-alkylaromatic compounds, such as ethylbenzene and cumene are valuable commodity chemicals which are used industrially for the production of styrene monomer and phenol respectively. Ethylbenzene may be produced by a number of different chemical processes, but one process which has achieved a significant degree of commercial success is the vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. In the commercial operation of this process, the polyalkylated benzenes, including both polymethylated and polyethylated benzenes, which are inherently co-produced with ethylbenzene in the alkylation reactor, are transalkylated with benzene to produce additional ethylbenzene either by being recycled to the alkylation reactor or by being fed to a separate transalkylation reactor. Examples of such ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge), and U.S. Pat. No. 4,016,218 (Haag).
More recent focus has been directed at liquid phase processes for producing ethylbenzene from benzene and ethylene since liquid phase processes operate at a lower temperature than their vapor phase counterparts and hence tend to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 describes the liquid phase synthesis of ethylbenzene with zeolite beta, whereas U.S. Pat. No. 5,334,795 describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene.
Cumene has for many years been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. More recently, however, zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
Other molecular sieves known for use as liquid phase alkylation and transalkylation catalysts include MCM-36 (see U.S. Pat. No. 5,258,565), MCM-49 (see U.S. Pat. No. 5,371,310) and MCM-56 (see U.S. Pat. No. 5,453,554).
Known methods of synthesizing, such as, alkylation or transalkylation catalysts, usually comprise a step of drying them in a deep fixed bed calciner (e.g., having a catalyst height of 1 meter or more) with flowing air or nitrogen.
It is said that one method for modifying the Relative Activity of the final catalyst is by steaming. U.S. Pat. Nos. 4,663,492; 4,594,146; 4,522,929; and 4,429,176 describe conditions for the steam stabilization of zeolite catalysts which can be utilized to steam-stabilize the catalyst. The steam stabilization conditions include contacting the final catalyst with, e.g., 5-100% steam at a temperature of at least about 300° C. (e.g., 300-650° C.) for at least one hour (e.g., 1-200 hours) at a pressure of 101-2,500 kPa. In a more particular embodiment, the final catalyst can be made to undergo steaming with 75-100% steam at 315° C.-500° C. and atmospheric pressure for 2-25 hours. In accordance with the steam stabilization treatment described in the above-mentioned patents, the steaming of the catalyst can take place under conditions sufficient to initially increase the Alpha Value of the catalyst and produce a steamed final catalyst having a peak Alpha Value. If desired, steaming can be continued to subsequently reduce the Alpha Value from the peak Alpha Value to an Alpha Value, which is substantially the same as the Alpha Value of the unsteamed final catalyst.
U.S. Pat. No. 8,222,468 provides a process for conversion of feedstock comprising organic compounds to desirable conversion product at organic compound conversion conditions in the presence of catalyst comprising an acidic, porous crystalline material and having a Proton Density Index of greater than 1.0, for example, from greater than 1.0 to about 2.0, e.g., from about 1.01 to about 1.85. The acidic, porous crystalline material of the catalyst may comprise a porous, crystalline material or molecular sieve having the structure of zeolite Beta, an MWW structure type material, e.g., MCM-22, MCM-36, MCM-49, MCM-56, or a mixture thereof. In this disclosure, a method for producing the catalyst for use is also provided comprising the steps of: (a) providing a first, untreated catalyst, i.e., one not having been treated according to steps (b) and (c) of this method, comprising an acidic, porous crystalline material, said first, untreated catalyst having a first hydration state measured in mmol of protons per gram of catalyst; (b) contacting the first, untreated catalyst of step (a) with water in liquid or gaseous form, at a contact temperature of up to about 500° C., such as from about 1° C. to about 500° C., preferably from about 1° C. to about 99° C., for a contact time of at least about 1 second, preferably from about 1 minute to about 60 minutes, to generate a second catalyst having a second hydration state measured in mmol of protons per gram of catalyst, said second hydration state being greater than said first hydration state, i.e., the product of step (b) has a higher proton density than the step (a) catalyst; and (c) drying the second catalyst resulting from step (b) at a drying temperature of up to about 550° C., preferably from about 20° C. to about 550° C., more preferably from about 100° C. to about 200° C., for a drying time of at least about 0.01 hour, preferably from about 0.1 to about 24 hours, more preferably from about 1 to about 6 hours, to generate the catalyst composition having a third hydration state measured in mmol of protons per gram of catalyst between said first and second hydration states. The step (c) product will have a Proton Density Index of greater than 1.0, for example, from greater than 1.0 to about 2.0, e.g., from about 1.01 to about 1.85.
According to the invention, it has now been found that drying the catalyst, after which being contacted with water, under certain conditions, such as temperature, can result in a difference in selectivity to mono-alkylaromatic compounds of the alkylation or transalkylation catalysts. It has been found that drying the catalysts with a small catalyst deposit height at a low temperature is effective in improving the catalyst selectivity to the mono-alkylaromatic compound. This novel method of the present disclosure provides an efficient and convenient way for treating the aromatic alkylation or transalkylation catalysts to improve catalyst selectivity without substantially deteriorating the catalyst activity.